This is fantastic for rolling multiple d10s simultaneously or for when you need a really big number, but by switching things up, you can do other things with your box o’dice.
If you have a battle set up with a bunch of mooks, filling your dice box with the required dice to roll multiple attacks simultaneously can speed things up a lot. Even if they have different initiative, you can roll them all at once and read them off as needed. It can be difficult to put more than one of some types of dice in a single compartment and tell which order to use them, but using small dice of differing colors can make that more manageable.
Just for You:
Most people use only a handful of dice each session, and make the same rolls repeatedly, so it seems silly to not take advantage of that. Below is a die box tailored specifically to my DnD 4e character. All I have occasion to do is make a skill roll with a d20, or make an attack with my d20 plus 1 or 2 d4s or d6s. Sometimes I also add the two small red sneak attack dice. That’s pretty much it. I’ve filled the remaining spaces with the remaining die types “just in case” but I rarely, if ever, use them. Alternately, I could fill those spaces with my mini, or commonly used counters.
Just like as a player, you rarely roll more than a few dice, as a GM there are some dice you need much more often than others. Try putting rolls you use a lot, or common dice combinations together, then filling the remaining slots with the rest of the dice you only occasionally use.
One of Every Die:
By filling the box with one of every die (and a second d10) you can roll any die and any combination of non-duplicate dice with a single shake, saving time and preventing lost dice to boot. This is a good all-around use for your D10million.